Look, it's not rocket science.

Someone drafted the memo. The memo is real and it shows the kind of people who reside in the White House. The admin considered it and either passed on it for the time being or it' still mulling the proposal over.

Some bureaucrat or opposing member of the staff came across it and leaked it in order to damage the proposal and the one who made it.

The White House denies it because that's what's you do with a policy you haven't decided upon.

But all the same, the cause of alarm, i.e. the fact that immigration hardliners are very much part of the White House inner circle remains.